1. Field of the Invention
Embodiments of the present invention generally relate to integrated circuit packages. More particularly, embodiments of the present invention relate to integrated circuit packages having bypass capacitors coupled to the bottom of the package substrate and supporting surface mounting technology.
2. Related Art
Typically, the integrated circuit chip die is not directly attached to a printed circuit board assembly. Rather, the integrated circuit chip die is attached to a top of a package substrate. Organic substrates and ceramic substrates are the most widely used types of package substrates. In general, the organic substrate is comprised of multi-layers of organic material while the ceramic substrate is comprised of multi-layers of ceramic material. The bottom of the package substrate usually has solder balls, pins, or other means to attach the integrated circuit package (which includes the integrated circuit chip die and the package substrate) directly to the printed circuit board assembly or directly to a socket that is attached to the printed circuit board assembly. Moreover, different techniques are used to couple bypass capacitors (also referred as decoupling capacitors) to the package substrate. The bypass capacitors are more effective if coupled to the bottom of the package substrate rather than to the top of the package substrate. The bypass capacitors placed between signal lines reduce the electrical noise of the signal lines. Additionally, the bypass capacitors placed between power line and ground line reduce power surges in the power and ground lines.
FIG. 1 illustrates a cross-sectional view of a first conventional electronic assembly 100, showing one method of coupling bypass capacitors to the bottom of the package substrate 20. The conventional electronic assembly 100 includes a chip die 10, a package substrate 20 that is a ceramic substrate 20, and a printed circuit board assembly (PCBA) 30 usually comprised of an organic material. The chip die 10 is coupled to the top of the ceramic substrate 20 in a flip-chip configuration. Moreover, solder bumps 12 couple the chip die 10 to the ceramic substrate 20. Additionally, the integrated circuit package 50 is comprised of the chip die 10 and the ceramic substrate 20.
The ceramic substrate 20 includes an array of solder balls 22 at the bottom. Hence, the integrated circuit package 50 is a BGA (Ball Grid Array) package. The solder balls 22 facilitate surface mounting the integrated circuit package 50 to the PCBA 30. Additionally, the ceramic substrate 20 has cavity1 and cavity2 formed in the bottom of the ceramic substrate 20. Bypass capacitor1 is coupled and located in cavity1 while bypass capacitor2 is coupled and located in cavity2, allowing the integrated circuit package 50 to be surface mounted to the PCBA 30.
The first conventional electronic assembly 100 has several deficiencies. Organic substrates are less expensive than ceramic substrates. However, forming cavities for the bypass capacitors in the bottom of an organic substrate is expensive and not practical for organic substrates. Moreover, the thermal expansion properties of the ceramic substrate 20 and the PCBA 30 are mismatched, putting great stress on the solder balls 22 and reducing reliability. The thermal expansion rate of the PCBA 30 is greater than the thermal expansion rate of the ceramic substrate 20.
FIG. 2 illustrates a cross-sectional view of a second conventional electronic assembly 200, showing a second method of coupling bypass capacitors to the bottom of the package substrate 20. The second conventional electronic assembly 200 includes a chip die 10, a package substrate 20 (can be organic or ceramic), a socket 60, and a printed circuit board assembly (PCBA) 30 usually comprised of an organic material. Here, the chip die 10 is coupled to the top of the package substrate 20 in a flip-chip configuration. However, the chip die 10 can also be coupled to the top of the package substrate 20 in a wire bonding configuration. Moreover, solder bumps 12 couple the chip die 10 to the package substrate 20. Additionally, the integrated circuit package 50 is comprised of the chip die 10 and the package substrate 20.
The package substrate 20 includes an array of solder balls 22 at the bottom. Hence, the integrated circuit package 50 is a BGA (Ball Grid Array) package. The solder balls 22 facilitate mounting the integrated circuit package 50 to the socket 60. Alternatively, the package substrate 20 can have pins rather than solder balls 22.
Moreover, bypass capacitors 71 and 72 are coupled to the bottom of the package substrate 20. A cavity 65 is milled out in the center of the socket 60, which is mounted to the PCBA 30 via pins 40. The cavity 65 provides clearance to enable the bypass capacitors 71 and 72 to be coupled to the bottom of the package substrate 20.
Unfortunately, the second conventional electronic assembly 200 also has several deficiencies. Use of the socket 60 increases costs. Moreover, the height of the socket 60 and PCBA 30 combination is too large for many applications.